Inferior vena cava filters, also called IVC filters or Greenfield filters, are medical devices that are implanted into the inferior vena cava to prevent pulmonary emboli. They work by trapping emboli while still permitting the flow of blood, thereby preventing an embolus from sealing off a vessel. IVC filters are used if anticoagulation is ineffective or contraindicated.
IVC filters are inserted via the blood vessels (i.e., placed endovascularly). Known filters can be compressed into thin catheters permitting access to the venous system via the femoral vein or the internal jugular vein. A catheter is guided into the IVC using fluoroscopic guidance. The filter is pushed through the catheter and deployed into the desired location. IVC filters are usually positioned just below the junction of the IVC and the lowest renal vein.
IVC filters may be permanent or retrievable. Retrievable filters have a configuration that allows them to be pulled back into a catheter or sheath to be removed. In either case, these filters also include structure to anchor the filter in place within the vena cava. Typical features include elongate diverging anchor elements called second extension elements. These frequently have hooked ends that penetrate the vessel wall to prevent migration within and along the vessel. Some types of filters also have first extension elements which contact the wall of the vessel at a point that is axially displaced from the point of contact by the second extension elements. This apposition helps to keep the filter axially oriented (i.e., prevents tipping) and centered.
U.S. Pat. No. 4,494,531 to Gianturco describes a filter with multiple strands of shape memory wire which are interconnected and wadded together to form a mesh. The filter has projections at either end of the mesh that anchor it within the inferior vena cava. Each anchor has a wire loop act as a stop to prevent the anchors from penetrating too deeply.
U.S. Pat. Nos. 4,643,184 and 4,272,823 to Mobin-Uddin describe a filter with a central cylindrical column which interconnects a pair of corollas of elongate hoops forming two tiers of metal wire. The hoops are each inclined outwardly from the column. Each of loops is formed of two wires with the outer ends of the wires being bent toward each other to form short circumferentially extending portions and then 180° in the same plane to form oppositely extending circumferential portions. The extreme ends of the wires are bent radially outwardly into hooks. The wires of each loop may be joined at the crowns of the open loops to cause them to hook together. The circumferentially bent portions at the ends of the hoops form stops or barriers which prevents the hooks at the ends from penetrating the wall of the passageway (artery) sufficient to prevent a puncture.
U.S. Pat. No. 5,755,790 to Chevillon, et al. describes a filter with a central portion and two corollas connected by the central portion. The upstream corolla has spines with flat shoes at their ends that contact the arterial wall. The support corolla has folded elongate hoops that terminate in v-shaped portion that also contacts the arterial wall downstream of the upstream shoes. The device is removable and does not penetrate the arterial wall.
U.S. Pat. Nos. 6,007,558, 6,258,026, and Publication No. 2005/0234503 to Ravenscroft, et al. describe a filter with first and second corollas joined at the downstream end like the ribs of an umbrella but with one set of ribs forming the downstream corolla and one set forming the upstream corolla. The upstream corolla ribs have hooks at their ends. The downstream corolla rib ends are turned toward the axial center of filter, thereby preventing the ends from projecting into the arterial walls.
U.S. Pat. Nos. 6,231,589 and 6,706,054 to Wessman, et al. describe a filter with first and second corollas connected by a central cylindrical member forming two corollas each with ribs extending radially and upstream. The upstream corolla ribs and downstream ribs have similar structures which bifurcate toward their ends. Barbs are located at the points where the upstream ribs bifurcate to anchor the filter in the artery.
U.S. Pat. No. 6,972,025 to WasDyke describes a filter with first and second corollas joined at the downstream end like the ribs of an umbrella but with one set of ribs forming the downstream corolla and one set forming the upstream corolla. The upstream corolla ribs have hooks at their ends. The downstream corolla rib ends are rounded and made of bioabsorbable material.
U.S. Pat. No. 7,037,320 to Brady, et al. describes a filter with a support which has round wires the form hoops. The hoop formed by the wires ensures that in the expanded position, a filter body will be supported by the support frame in apposition with the interior wall of the blood vessel. The wires have a strain distributing loop that allows the diameter of the hoop to self-adjust to the blood vessel size. The strain relieving loop enhances the compliance of bend points in the circumferential seal of the hoop against the vessel wall.
US Patent Publication No. 2005/0045183 describes a filter with a corolla with extensions having wall-penetrating hook or barb. The extensions form a single array at a single longitudinal location, like the spokes of an umbrella or the legs of a spider.
US Patent Publication Nos. 2006/0030875 and 2006/0106417 to Tessmer describe a filter with first and second corollas joined at the downstream end like the ribs of an umbrella but with one set of ribs forming the downstream corolla and one set forming the upstream corolla. The upstream corolla ribs have hooks at their ends. The downstream corolla rib ends are turned toward the axial center of filter, thereby preventing the ends from projecting into the arterial walls.
US Patent Publication No. 2006/0178695 to Decant, et al, shows a filter with a corolla with extensions having wall-penetrating hook or barb. The extensions form a single array at a single longitudinal location.
U.S. Pat. Nos. 5,669,933 and 5,836,968 to Simon show a filter with a basket and extensions that curve toward the downstream end of the channel.
U.S. Pat. No. 6,468,290 to Weldon, et al, shows a filter with an array of extensions that have hooks that curve toward the downstream direction.
There are a number of conflicting issues concerning the design of vena cava filters. Filters that are intended to be removed must hold their position in the vena cava but in a manner that does not cause undue damage to the vena cava wall. Also, the design features that hold the filter in place must also not promote tissue growth that would make it difficult to remove the filter atraumatically. The filter may need to be self-orienting to some extent as well so there may need to be a bias against the walls of the vena cava to provide this quality.